Microelectronics manufacturers utilize a number of different species of gas during the processing of wafers, which are fundamental to the manufacture of semi- and superconductor devices. Wafer processing generally involves discrete steps of growing one or more layers of various materials on a wafer and/or doping particular regions of existing layers to change the electrical characteristics of the original material. Growing a new layer and doping an existing layer typically involves flowing one or more gases into a processing chamber to effect the desired result. Some wafer processing steps require flowing only one type of gas into the processing chamber. However, other wafer processing steps require flowing two or more types of gas simultaneously with one another. Typically, only a portion of the gas(es) flowed through the processing chamber is actually consumed by the particular process. The remaining portion of the gas(es) exits the processing chamber as exhaust gas.
Generally, the exhaust gas must be processed and/or contained so that it does not contaminate the environment. When only a single gas is used for a particular processing step, the processing and/or containment of the gas is generally straightforward, requiring only one type of apparatus, such as a collection tank or scrubber. When two or more gases are used, however, processing the exhaust gases can be more difficult, particularly when one of the gases is not compatible, or interferes, with the processing of one or more of the other gases.
For example, in trench processing of wafers during the manufacture of DRAM-type memory it is desirable to simultaneously flow a carrier gas, such as silane, and a doping gas, such as arsine, into the wafer processing chamber. Since each of these gases is not used up completely during processing, the unused portions of these gases must be exhausted from the processing chamber and disposed of properly.
The abatement of arsine is a particular problem due to its high toxicity as a hydride and the high toxicity of the arsenic component of arsine. A preferred method of abating arsine is to use a dry resin-type adsorption system comprising a replaceable resin canister. Unfortunately, the relatively large amount of silane present in the exhaust gas is also collected in the resin canister, drastically reducing its useful life and increasing wafer processing cost due to the need to replace the resin canisters more often than if only the arsine were being collected in the resin canister.
Other abatement methods, such as combustion and wet-type scrubbers, are generally not desirable for abating arsine. The combustion of arsine creates a toxic particulate that is difficult to collect and dispose of. Scrubbing arsine with a wet-type scrubbers is not desirable since it would create a large amounts of toxic water that is difficult to dispose of. In addition, water scrubbing is not compatible with silane, which is insoluble and non-reactive with water.
In view of the foregoing, a need exists for an improved exhaust gas scrubbing system, and this solution is provided by the following invention.